Dell Studio One "Sleep" mode

I'm having issues with my All-in-one Studio One. Most of the time it will not go into the sleep mode in the time I have set for it to do it. Then, sometimes it does go into "Sleep" but I can't arouse it! If I move the mouse or hit the power button for a second, it will show the start up screen for a couple of seconds and then go blank. However, something is going on in the background because I can here the Windows sounds going on. But no screen! In order to get the screen again, I have to hard shut off the computer and restart it. It goes through the entire Windows 7 startup process and then starts working. I can't imagine that it is good to be doing a hard shutdown and restart nearly every time it goes to "Sleep". Nor do I like to have the screen going through my "pictures" file for hours because it won't go into "sleep". Something is wrong but what?